Highly selective formation of [4+2] and [4+3] cycloadducts of tetrahydroindenes generated in situ from a (1-alkynyl)carbene tungsten complex by the metalla-1,3,5-hexatriene route

DOI: 10.1002/1521-3765(20011203)7:23<5070::AID-CHEM5070>3.0.CO;2-6

Source and publish data:

Chemistry - A European Journal p. 5084 - 5093 (2001)

Update date:2022-08-03

Topics:

Authors:

Wu, He-Ping

Aumann, Rudolf

Froehlich, Roland

Wibbeling, Birgit

Kataeva, Olga

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Article abstract of DOI:10.1002/1521-3765(20011203)7:23<5070::AID-CHEM5070>3.0.CO;2-6

1-Amino-3-ethoxytetrahydro-3aH-indenes 8 can be readily generated together with pentacarbonyl(pyridine)-tungsten in a template induced three-component reaction of [(1-cyclohexenyl)-ethynyl]carbene tungsten complex 1 with secondary amines 2a-d and pyridine. Even though the compounds 8 are thermally quite unstable and undergo a fast rearrangement to tetrahydro-7aH-indenes 7, they can be trapped by formation of (rather strained) [4+2] cycloadducts 12 with maleimide 11. If 1-amino-3-ethoxytetrahydro-3aH-indenes 8 are generated in the presence of electron-poor alkynes 2a and 2b, they undergo a 1,5-shift to give tetrahydro-7aH-indenes 7, which in turn afford [4+2] cycloadducts 4a-d. Condensation of 1-tungsta-1,3,5-hexatrienes (3E)-5a-d with 1-metalla-1,3-butadienes 14 (M= Cr, W) give [4+3] cycloadducts 15a-e of tetrahydro-7aH-indenes 7 in good yields with high regio- and stereoselectivity.

Full text of DOI:10.1002/1521-3765(20011203)7:23<5070::AID-CHEM5070>3.0.CO;2-6

FULL PAPER

S-Position Isomers of BEDT-TTF and EDT-TTF: Synthesis and Influence of

Outer Sulfur Atoms on the Electrochemical Properties and Crystallographic

Network of Related Organic Metals

Pie¬trick Hudhomme,* Soazig Le Moustarder, Christophe Durand, Nuria Gallego-Planas,

Nicolas Mercier, Philippe Blanchard, Eric Levillain, Magali Allain, Alain Gorgues, and

Ame¬de¬e Riou^[a]

Dedicated to Prof. Guy Duguay on his retirement.

Abstract: The synthesis and character-

ization of new modified tetrathiafulva-

lenes (TTF), the S-position isomers of

BEDT-TTF and EDT-TTF, are de-

scribed. The synthetic strategy present-

ed in this work is based on an efficient

and unprecedented two-step sequence

for the conversion of a vicinal bis(hy-

droxymethyl) functionality into a disul-

fide ring. Different routes are discussed

in terms of efficiency for the synthesis of

the symmetric S-position isomer of

BEDT-TTF and that of EDT-TTF. Their

electrochemical properties are com-

bined with data obtained from UV/Vis

spectroscopy and orbital calculations,

and the electronic influence of periph-

eral sulfur atoms on the neutral and

oxidized species is discussed. The intro-

duction of these outer sulfur atoms at

the periphery of the TTF core gives rise

to specific intermolecular S ¥¥¥ S interac-

tions in the correspondingorganic ma-

terials. Crystallographic studies of radi-

cal cation salts synthesized upon electro-

crystallization clearly showed that the

network obtained is dictated by the

outer sulfur atoms, which are responsi-

ble for a characteristic and unprecedent-

ed ™windmill∫ array.

Keywords: BEDT-TTF isomers

crystal engineering ¥ organic materi-

als ¥ sulfur heterocycles ¥ tetrathia-

fulvalene

One of the most successful strategies for improving the

electroconductive properties of related materials relies on the

introduction of sulfur atoms at the periphery of the TTF

skeleton. In particular, the well known sulfur-rich p-donor

bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) has

Introduction

Considerable interest is currently beingdevoted to tetrathia-

fulvalene (TTF) derivatives as highly promising p-electron

donors and versatile systems presentingapplications in many

areas,^[1]as well as to the elaboration of organic materials that

display unusual electrical properties.^[2]Consequently, rapid

progress has been observed in this field thanks to various

chemical modifications of the TTF framework.^[3]Neverthe-

less, the excessive one-dimensional character of organic

metals in the TTF series is responsible for limitations in their

transport properties (Peierls distortions). The enhancement

of the dimensionality is thus considered an important goal for

stabilizingthe metallic state at low temperatures and, in some

cases, to give rise to superconductivity.

produced two-dimensional conductors and a large number of

[4]

superconductingradical cation salts

endowed with the

highest critical temperatures (Tc) in that series. In their solid

state structures, strongsulfur sulfur intermolecular interac-

tions play an essential role in the well-defined two-dimen-

sional character.^[5]

We were interested in chemical modification of ET in order

to modify the two-dimensional molecular network, thus

developinga novel array of molecular conductors. From this

viewpoint, we have concentrated our efforts on modifyingthe

positions of the peripheral sulfur atoms, with the aim of

establishingspecific S ¥¥¥ S contacts in the molecular arrange-

ment of related materials. Such intermolecular interactions

have also been proposed for p-donors that have peripheral

sulfur atoms,^[6]such as bis(ethylenethio)TTF (BET-TTF).

Furthermore, the ability to form two-dimensional organic

(super)conductors is not limited to the radical cation salts of

symmetric TTF derivatives: dissymmetric donors are also

[a] Prof. P. Hudhomme, Dr. S. Le Moustarder, Dr. C. Durand,

Dr. N. Gallego-Planas, Dr. N. Mercier, Dr. P. Blanchard,

Dr. E. Levillain, M. Allain, Prof. A. Gorgues, Prof. A. Riou

Ingenierie Moleculaire et Materiaux Organiques

UMR 6501 Universite d×Angers

2 Boulevard Lavoisier, 49045 Angers (France)

Fax : (33)2-41-73-54-05

E-mail: pietrick.hudhomme@univ-angers.fr

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Chem. Eur. J. 2001, 7, No. 23

5070 5083

very attractive because of their tendency to crystallize into

centrosymmetric dimers, thus favoringthe so-called two-

dimensional k-phase network,^[7]considered to be the passport

to the generation of superconducting mixed valence salts in

the TTF series.

1: DIET

Recently, we have been interested in the unprecedented

dissymmetric^[8]and symmetric^[9]outer S-position isomers of

BEDT-TTF. We now report the syntheses of DIET (Dissym-

metric Isomer of ET, 1) and SIET (Symmetric Isomer of ET, 2)

as well as their spectroscopic characterizations, electrochem-

ical and orbital properties. We have also extended our

synthetic approach to the development of the corresponding

S-position isomers of EDT-TTF and DMTEDT-TTF: com-

pounds 3 (named IEDT-TTF, for Isomer of EDT-TTF) and 4,

respectively (Scheme 1). This new disulfide functionality in

the TTF series, common to targets 1 4, appears to be of

particular interest in understandingthe nature of resulting

intermolecular interactions in the crystal engineering of the

molecular materials.

BEDT-TTF or ET

2: SIET

EDT-TTF

3: IEDT-TTF

CH₃S

DMTEDT-TTF

Scheme 1. Target molecules as S-position isomers of BEDT-TTF, EDT-

TTF, and DMTEDT-TTF.

Results and Discussion

Synthesis of DIET and the S-position isomer of DMTEDT-

TTF (4): Historically, we have focused our attention on

the synthesis of the dissymmetric targets 1 and 4 (Scheme 3).^[8]

Compounds 5a and 5b were prepared by following

our previously reported synthetic strategy.^[10]The tri-

methylphosphite-mediated cross-couplingof the two corre-

sponding2-(thi)oxo-1,3-dithiole moieties 7 and 8 afforded

2,3-bis(methyloxycarbonyl)TTFs 9a and 9b, respectively, in

good yields. Further reduction of the ester functions was

cleanly achieved by use of sodium borohydride/zinc chloride

in THF under reflux to give 2,3-bis(hydroxymethyl)TTFs 5a

and 5b.

Definition of the strategy: The most appropriate retrosyn-

thetic analysis to reach disulfide compounds consists of two

successive functional modifications with the thioester group

as an intermediate (Scheme 2a). By usingthis strategy, two

different routes can be envisaged: i) the transformation of 2,3-

bis(hydroxymethyl)TTFs 5a c, first developed by our

group^[10]for the synthesis of dissymmetric targets, or, specif-

ically for the synthesis of SIET, tetrakis(hydroxymethyl)TTF

5d,^[11]and ii) the disconnection of the TTF central double

bond, leadingto 2-thioxo-4,5-bis(hydroxymethyl)-1,3-dithiole

^[11b]as startingmaterial (Scheme 2b).

We then investigated the generation of a good leaving

group from the 2,3-bis(hydroxymethyl)TTF, in order to

activate the nucleophilic substitution for conversion of the

Abstract in French: Les isomõres de position des atomes de

soufre pÿriphÿriques du ´fameuxª BEDT-TTF ont ÿtÿ syn-

thÿtisÿs et ont ÿtÿ nommÿs DIET et SIET, respectivement, pour

isomõres dissymÿtrique et symÿtrique de BEDT-TTF. La

mÿthodologie de synthõse du pont disulfure terminal a ÿtÿ

ÿtendue, plus spÿcifiquement pour prÿparer l×isomõre de EDT-

TTF. Ainsi, la stratÿgie synthÿtique dÿveloppÿe fait en particu-

lier appel ‡ une rÿaction originale d×activation des fonctions

alcools des bis(hydroxymÿthyl)TTF suivie d×un accõs rapide au

pont disulfure cyclique. Les propriÿtÿs ÿlectrochimiques sont

ÿgalement prÿsentÿes, complÿtÿes par les calculs thÿoriques et

propriÿtÿs optiques des donneurs ‡ l×ÿtat neutre ou oxydÿ.

L×influence de la position des atomes de soufre pÿriphÿriques

est clairement ÿtablie en comparant les structures cristallogra-

phiques des diffÿrents sels de cations radicaux de st˙chiomÿtrie

ÿquivalente issus de ces donneurs-p isomõres de position.

alcohol function into a thioester.^[12]This problem was

[13]

efficiently solved by usingthe Mitsunobu reaction.

The

diethyl azodicarboxylate/triphenylphosphine (DEAD/PPh₃)

complex reacted with 2,3-bis(hydroxymethyl)TTF (5), which

allowed the activation of the alcohol function. Substitution

could then occur in the presence of an acidic reagent, such as

thioacetic acid. Followingthe experimental conditions pre-

viously reported for this type of reaction,^[14]a mixture of

dialcohol 5a and thioacetic acid in THF was added dropwise

to the DEAD/PPh₃complex in THF at 08C to give the

bis(thioester)TTF 10a in 58% yield. However, application of

this Mitsunobu reaction to the 2,3-bis(hydroxymethyl)-6,7-

(ethylenedithio)TTF (5b) was unsuccessful because of the

well-known sensitivity of the ethylenedithio bridge to bases

and nucleophiles.^[15]To avoid this undesired reaction we

considered another means of activatingthe hydroxymethyl

group that involved N,N-dimethylformamide dineopentyl-

acetal.^[16]The analogous diethylacetal reagent was applied

successfully to 5a and 5b and was finally preferred because of

the easier subsequent purification of the bis(thioester)TTFs

10a and 10b, which were obtained in 58% and 60% yields,

respectively. The one-pot reaction was carried out by usingan

√

Ainsi, le role du pont disulfure dans l×organisation structurale

s×avõre dÿterminant dans la plupart des cas, et responsable d×un

arrangement tout ‡ fait original, dit ´en moulin ‡ ventª, au sein

duquel l×anion est localisÿ au centre de la cavitÿ et les donneurs

adoptant une organisation perpendiculaire les uns par rapport

aux autres.

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P. Hudhomme et al.

FULL PAPER

diffraction.^[8]DIET (1), on the

other hand, showed poor solubil-

ity in CH₂Cl₂, estimated as ten

times lower than that of BEDT-

TTF itself. Consequently, com-

pound 1 was first obtained as an

analytically pure sample by filtra-

tion (88%). In order to obtain

crystals of the high purity neces-

sary to accomplish further electro-

crystallization experiments, we

performed the purification using

a short column of Florisil, with

CS₂as the eluent. Nevertheless,

the best purification appeared to

be by Soxhlet extraction with CS₂

for several days, affordingpure

orange microcrystals of DIET.

SCOCH₃

a : R = SCH₃

b : R-R = SCH₂CH₂S

c : R = H

disconnection

d : R = CH₂OH

X = O, S

Scheme 2. Retrosynthetic scheme and startingmaterials.

6 a

excess of both activatingreagent and thioacetic acid, and by

followingthe proposed mechanism (Scheme 3).

Synthesis of SIET: For the target SIET (2), we first considered

the classical symmetric couplingreactions from correspond-

ing2-(thi)oxo-1,3-dithioles 13 (Scheme 4).^[9]Initially, for the

synthesis of 11, our efforts were concentrated on the reactions

previously applied in the TTF series for the preparation of 1

and 4. After many experiments, the best results were obtained

when the Mitsunobu reaction was used for 6a and the

activation with N,N-dimethylformamide diethyl acetal for 6b.

In both cases, compounds 11a and 11b were accompanied by

undesired by-products and yields remained unsatisfactory

(32% and 52%, respectively). The alternative route consisted

of performingan easier nucleophilic substitution on analo-

gous 4,5-bis(bromomethyl)-2-(thi)oxo-1,3-dithioles. Thus, diol

6a was readily converted into 12a by usingphosphorus

tribromide, in 94% yield.^{[9, 21]}Parallel to our work, the

synthesis of 12a was also achieved in 70% yield by use of

CBr₄/PPh₃in a similar reaction.^[22]Our strategy was then

In order to reach the target disulfides, we initially prepared

the dithiols^[17]in 91% and 96% yields by reduction of 10a and

10b with DIBAl-H, respectively.^[8]Further oxidation with

DEAD,^[18]iodine, or 2,2'-dithiobis(benzothiazole)^[19]resulted

in 1 and 4. However, this strategy suffered from the modest

yields (30 50%) of this last step. Furthermore, we found that

reduction of the bis(thioester)TTF, followed by oxidation to

disulfide could be carried out with satisfactory yields in a one-

pot reaction. Reduction was accomplished with sodium

borohydride in the presence of lithium chloride in THF under

reflux, and subsequent treatment with an aqueous solution of

ammonium chloride efficiently afforded compounds 1 and

4.^[20]The S-position isomer of DMTEDT-TTF was easily

purified by chromatography on silica gel and recrystallized

from CH₂Cl₂/petroleum ether (93% yield). Single crystals of

this disulfide compound 4 were obtained and studied by X-ray

CO₂CH₃

CH₂OH

9a, b, c

7a : R,R = SCH₃

7b : R-R = SCH₂CH₂S

7c : R,R = H

5 a, b, c

CH₂SCOCH₃

10 a, b, c

1 : R-R = SCH₂CH₂S

4 : R,R = SCH₃

3 : R,R = H

OEt

CH₃

SCOCH₃

(-EtOH, -DMF)

(-EtOH)

Scheme 3. Synthetic strategy for DIET and the S-position isomers of DMTEDT-TTF and EDT-TTF. a) D, P(OMe)₃(9a: 59%, 9b: 60%, 9c: 20%);

b) NaBH₄/ZnCl₂, D, THF (5a: 83%, 5b: 70%, 5c: 61%); c) Method A: DEAD/PPh₃, CH₃COSH, THF (10a: 58%, 10c: 51%) or Method B:

Me₂NCH(OEt)₂, CH₃COSH, D, CH₂Cl₂(10a: 59%, 10b: 60%); d) NaBH₄/LiCl, D, THF then NH₄Cl/H₂O (1: 88%, 4: 93%, 3: 28%).

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Chem. Eur. J. 2001, 7, No. 23

Isomers of Tetrathiafulvalenes

5070 5083

SCOCH₃

MeS

CF₃SO₃

6a X = S

6b X = O

11a, b

e) or f)

12a, b

SCOCH₃

CH₃OCS

SCOCH₃

(X = S)

13a, b

BF₄

SIET 2

Scheme 4. Different synthetic strategies for the symmetric S-position isomer of BEDT-TTF (SIET). a) DEAD/PPh₃, CH₃COSH, THF (11a: 32%) or

Me₂NCH(OEt)₂, CH₃COSH, CH₂Cl₂(11b: 52%); b) Hg(OAc)₂, AcOH/CHCl₃(44%), c) PBr₃, THF/CCl₄(12a: 94%, 12b: 62%); d) CH₃COSH, THF, Py

(11a: 94%, 11b: 98%) or CH₃COS^ÀK , THF (11a: 91%, 11b: 89%); e) NaBH₄/LiCl, then NH₄Cl/H₂O (13a: 78%); f) MeO^ÀNa , MeOH then I₂/ether (13b:

85%); g) D, P(OMe)₃(5%); h) CF₃SO₃Me, CH₂Cl₂(98%); i) NaBH₄, iPrOH/CH₃CN (91%); j) HBF₄, Ac₂O (quantitative); k) Et₃N, CH₃CN (62%);

l) MeO^ÀNa , MeOH/DMF (63%); m) Ref. [11b] MeI, THF (98%), NaBH₄, MeOH (90%), HBF₄, Ac₂O, then Et₃N, CH₃CN (77%), KOH, MeOH/THF/H₂O

(92%); n) Me₂NCH(OEt)₂, CH₃COSH, D, THF(63%).

applied to the preparation of 12b in 62% yield, but the easiest

route to this compound remained the bromination of 4,5-

dimethyl-2-oxo-1,3-dithiole by using N-bromosuccinimide

(NBS).^[23]After subsequent treatment of 12a or 12b with

thioacetic acid (or potassium thioacetate), this route proved

to be applicable on a large scale, compounds 11a and 11b

beingproduced in excellent yields in both cases. Two different

reactions were developed to obtain disulfide 13. The previous

method with sodium borohydride/lithium chloride followed

by aqueous ammonium chloride solution treatment was

applied successfully to give 13a in 78% yield. We extended

the development of the cleavage of the dithioester groups by

consideringtheir methanolysis. Thus, treatment of 11b with

sodium methoxide and subsequent treatment with iodine gave

disulfide 13b in 85% yield.

Unfortunately, attempts to achieve the trialkylphosphite-

mediated couplingreactions from 11a and/or 11b failed, as

did the dicobalt octacarbonyl method^[24]from 11a. In the case

of precursor 11a, trimethylphosphite couplingafforded the

correspondingoxo derivative 11b^[25]in 70% yield and TTF 14

in only 5% yield. Concerningthe couplingreaction from 13,

we noted the particular instability of the disulfide function

under such drastic experimental conditions. Many hypotheses

might explain this behavior: i) a possible retro-Diels Alder

reaction, resultingin the correspondingdienes upon heat-

ing.^[26]Indeed, this is argued for by the presence in the mass

spectra of peaks related to the dimethylidene[2H]-2-(thi)oxo-

1,3-dithiole(s) from 13a and 13b, dimethylidene[2H]TTF

from 1, 3, and 4, and also tetramethylidene[4H]TTF from 2,

firmed by Becher et al., who failed in the last step of their

attempt to reach molecule 4 by another strategy.^[28]

After these different failures in the couplingof 2-(thi)oxo-

1,3-dithioles 11, we considered an alternative route to reach

the symmetric TTF 14. Startingfrom 11a, the 1,3-dithiolium

cation salt 15 was first produced by methylation with methyl

triflate in quantitative yield. Reduction to 16 with sodium

borohydride in propan-2-ol/acetonitrile at 08C (91% yield)

was followed by dethiomethylation with fluoroboric acid in

acetic anhydride to produce 1,3-dithiolium tetrafluoroborate

17 in quantitative yield. This was immediately treated with an

excess of triethylamine in acetonitrile to give TTF 14 through

carbenoid couplingin 62% yield. Transformation of 14 into

the target S-position isomer of BEDT-TTF (2) was carried out

with reagents described above for the similar conversions of

10a and 10b to 1 or 4, but the yields were improved to 63% by

treatment with a methoxide solution in methanol/N,N-di-

methylformamide. The SIET compound was estimated to be

three times less soluble in CH₂Cl₂than BEDT-TTF itself, so it

could be efficiently purified by silica-gel column chromatog-

raphy with CS₂as the eluent. Thus, this route provides clean

and efficient access to the new symmetric S-position isomer 2

of BEDT-TTF.

Of course, we also studied the conversion of tetrakis(hy-

droxymethyl)TTF 5d into TTF 14. Because of its great

insolubility, the tetraalcohol was suspended in THF and

reacted progressively under reflux with an excess of N,N-

dimethylformamide, diethyl acetal, and thioacetic acid to

afford 14 in 63% yield after purification by column chroma-

tography on silica gel.

ii) the known reaction of trialkylphosphite with disulfides to

[27]

afford correspondingsulfides,

iii) the scission of the sul-

fur sulfur bond, which is favored under electrophilic, basic, or

nucleophilic conditions.^[27]This behavior was recently con-

Synthesis of the S-position isomer of EDT-TTF: Our previous

success with the trimethylphosphite cross-couplingof an

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equimolecular mixture of corresponding1,3-dithioles was

encouraging for a generalization of this strategy. When

applied to 7c and 8, the reaction effectively produced a

mixture of the three possible TTFs: two symmetric ones and

the expected dissymmetric product 9c. Unfortunately, the

dissymmetric TTF was obtained in this case only in a

moderate 20% yield.^[10c]Nevertheless, after reduction with

NaBH₄/ZnCl₂to afford the 2,3-bis(hydroxymethyl)TTF 5c in

61% yield, we were able to apply the Mitsunobu procedure to

prepare 10c in 51% yield. This strategy was preferred to the

acetal activation because of the easier purification of 10c

(Scheme 3). To avoid this unsatisfyingreaction, we used the

classical carbenoid couplingreaction ^[29]from the correspond-

ing1,3-dithiolium fluoroborate salts to produce symmetric or

dissymmetric TTF derivatives (Scheme 5).^[30]Such reactions

treatment with an aqueous solution of ammonium chloride.

The resultingyield of disulfide 3 was dramatically lowered

duringthe purification stage, however, no doubt because of its

low stability during silica-gel or Florisil column chromatog-

raphy (Scheme 3).

Electrochemical and spectroscopic properties; theoretical

calculations: The cyclic voltammograms of ET, DIET, and

SIET in CH₂Cl₂, and of EDT-TTF and IEDT-TTF in CH₂Cl₂/

CH₃CN showed two reversible one-electron processes; this

indicated successive generation of stable radical cations and

dications at apparent redox potentials E¹_appand E_a²_pp(Table 1).

The influence of the outer sulfur atoms on the redox

potentials was particularly apparent on the second redox

system and very weak on the first one. Indeed, the different

electronic

(inductive

and

mesomeric) effects of outer

sulfur atoms should be dis-

cussed.

SCOCH₃

To go into more detail, the-

oretical calculations at the ab

initio density functional level

with the Gaussian 98 pack-

age^[34]were performed in order

to investigate the influence of

the sulfur atoms on the molec-

ular structure and the electron-

ic properties of ET, DIET, and

SIET. Becke×s three-parameter

gradient-corrected functional

(B3LYP)^[35]with a polarized

BF₄

TTF

SCOCH₃

CH₃OCS

SCOCH₃

Et₃N/CH₃CN

Ph₃P

BF₄

SCOCH₃

P Ph₃

10c

BF₄

Scheme 5. Different routes to the S-position isomer of EDT-TTF.

31G* basis was used for a

full geometry optimization of

the three isomers ET, DIET, and SIET in the neutral, radical

cation, and dication states.

were carried out with both 1,3-dithiolium salts 17 and 18^[29]in

the presence of triethylamine and led to reproducible results

when the experimental conditions described herein were

followed. Thus, TTF (23%), dissymmetric compound 10c

(44%), and tetrakis(thioester)TTF 14 (18%) were succes-

sively separated by chromatography on silica gel. On the

other hand, we also tried to take advantage of an approach,

first developed by Cava^[31]and recently applied to the

synthesis of EDT-TTF,^[32]involvinga ™pseudo-Wittig∫ con-

densation of 1,3-dithiole-2-triphenylphosphonium salts as

ylide precursors, with 1,3-dithiolium salts as electrophiles. In

the case of the reaction involving 18 and 19 (obtained in 98%

yield by treatment of 17 with triphenylphosphine) in the

presence of triethylamine, the dissymmetric TTF 10c was

produced in 28% yield, accompanied by TTF (49%) and the

symmetric compound 14 (8%). As demonstrated previous-

ly,^[33]the instability of a startingtriphenylphosphonium salt in

the presence of a base produced an equilibrium between 19

and 17; this resulted in non-negligible amounts of symmetric

TTF. This observation was confirmed by the subsequent

reaction between 17 and 20, which afforded TTF (10%),

compound 14 (17%), and compound 10c (63%); this result

correspondingto the most efficient preparation of this

precursor of the S-position isomer of EDT-TTF.

Neutral molecules: No significant differences were shown for

the first oxidation peaks of neutral SIET, DIET, or BEDT-

TTF (Figure 1). Indeed, molecular orbital analysis of the

three isomers showed that the biggest HOMO coefficients

were mainly located on the central TTF core (the S₂C CS₂

fragment)^[36]and that the energy values for the three HOMOs

were very close (BEDT-TTF: À4.77 eV; DIET: À4.85 eV;

SIET: À4.92 eV). Because of the very small contribution of

the atomic orbital coefficients of the ethylenedithio group

Table 1. Cyclic voltammetry data for ET, DIET, and SIET^[a]for EDT-TTF

and IEDT-TTF.^[b]

Compound

E¹_app[mV]

E²_app[mV]

E¹_appÀ E²_app[mV]

DIET

SIET

EDT-TTF

IEDT-TTF

520

510

505

475

485

910

935

975

910

945

390

425

470

435

460

[a] c 10^À4molL^À1in 0.5 molL^À1TBAHP, CH₂Cl₂; Pt electrode, ref. Ag/

AgCl, scan rate 100 mVs^À1, 298 K. [b] c 1.4 Â 10^À3molL^À1in 0.2 molL^À1

TBAHP, CH₂Cl₂/CH₃CN (9:1); Pt electrode, ref. Ag/AgCl, scan rate

100 mVs^À1, 298 K. CH₃CN was added to avoid adsorption phenomena at

the electrode.

The final step was performed by usingsodium borohydride

and lithium chloride in THF under reflux, followed by

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Isomers of Tetrathiafulvalenes

5070 5083

to explain the small differences observed for the three

isomers, the sulfur atoms beingfurther out in SIET than in

BEDT-TTF. As previously shown by theoretical calculations

on tetrathiafulvalene derivatives in the neutral state, the

mesomeric effect of the sulfur atoms (S') had no significant

[38]

influence on their electron-donatingability.

The electronic properties were then studied to complete the

molecular-orbital analysis for these molecules. The UV/Vis

data showed that the experimental absorption wavelengths

for the three neutral molecules were fairly close in value

(Table 2). Calculations were performed by usingthe new

implementation of TD-DFT excitation energies,^[39]and gave

excitation energies that presented the same trend and showed

good numerical agreement for the three neutral isomers

(Table 2). As expected, the differences in the HOMO

LUMO gap estimated from electronic spectra for the neutral

state did not significantly differ for ET, DIET, and SIET (the

difference did not exceed 0.01 eV).

The optical properties of the radical cations and dications of

ET, DIET, and SIET were also investigated by UV/Vis and

near-IR spectroscopy, by addition of increasingamounts of

NOBF₄in CH₂Cl₂. Chemical oxidation resulted in the rapid

disappearance of the neutral TTF derivative and in the

development of new bands characteristic of the radical cation

and then of the dication (Table 2). As expected, the electronic

transitions of radical cation and dication were quasi-propor-

tional to E²_appfor each compound (Figure 3).

Figure 1. Comparison of BEDT-TTF, DIET, and SIET deconvoluted cyclic

voltammograms.

sulfur atoms (S') in the HOMOs of ET and DIET (0.1

coefficient), no significant mesomeric effect from the S-

substituents should be expected (Figure 2).^[37]No contribution

at all was found for the outer sulfur atoms (S'') of the disulfide

bridges of DIET and SIET.

Figure 3. Variation of the energy of cation radicals and dications of ET,

DIET, and SIET.

Figure 2. HOMO orbitals of ET (À4.77 eV; top), DIET (À4.85 eV;

middle), and SIET (À4.92 eV; bottom) in the neutral state.

Radical cations: The most important effect relatingto the

introduction of disulfide bridge(s) became apparent with the

second redox potentials, which shifted to more positive values

(Figure 1), an effect that was also apparent for IEDT-TTF

Consequently, only the electron-withdrawinginductive

character of the sulfur atoms should be taken into account

[a]

Table 2. Experimental and calculated optical data for ET, DIET, SIET and their correspondingoxidized states.

Compound

Neutral state

TD-DFT lowest

Radical cation state

Dication state

TD-DFT lowest

experimental

[nm]

experimental

TD-DFT lowest

experimental

[nm]

excitation energy [nm]

[nm]

excitation energy [nm]

DIET

SIET

322^[b]/346^[b]/458

311^[b]/338^[b]/466

314^[b]/327^[b]/474

420 (98 ! 100)

463 (98 ! 99)

480 (98 ! 99)

461^[b]/577/975

424^[b]/563/846

446^[b]/553/637

1028 (98a ! 100a)

885 (98a ! 100a)

620 (98a ! 100a)

718

559

406

840 (97 ! 98)

691 (95 ! 98)

462 (93 ! 98)

[a] addition of NOBF₄to 10^À4molL^À1in CH₂Cl₂at room temperature. [b] maxima in the vibronic structure. The molecular orbitals involved in each

transitions studied are indicated in brackets. Molecular orbitals 98 correspond to the HOMO for the neutral state, 98a and 98b to the HOMO and LUMO,

respectively, for the radical cation state, and 97 to the HOMO for the dication state.

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with respect to EDT-TTF (Table 1). Theoretical calculations

with the unrestricted-B3LYP functional were then performed

in order to study the differences in the optimized geometry

and the molecular structure of the three radical cations. The

optimized geometry found for the three isomers was perfectly

planar, and a significant contribution of the p-sulfur atoms

(S') from the ethylenedithio group appeared in the HOMO

crystallographic structure of the dication salts BEDT-TTF ¥

(ClO₄)₂or BEDT-TTF ¥ (BF₄)₂, in which no particular devia-

tion between the two rings was observed.^[42]In contrast,

DIET²and SIET²presented distortions from planarity of

15.468 and 26.798, respectively (Figure 5).

orbital in both ET and DIET , as well as the combination of

p-atomic orbitals of the TTF core (Figure 4).

Figure 5. HOMO orbitals of dications ET²(À12.24 eV; top), DIET²

(À12.08 eV; middle), and SIET²(À12.52 eV; bottom).

This structural peculiarity was unambiguously demonstrat-

ed with the DIET¥ CuBr₄dication salt, which was obtained by

chemical oxidation. In the crystallographic structure, this

DIET²was characterized by an important distortion from

planarity of 468 between the two dithiolium rings (Figure 6).

Figure 4. HOMO orbitals of radical cations ET (À8.39 eV; top), DIET

(À8.67 eV; middle), and SIET (À9.02 eV; bottom).

These changes could be explained by the existence of a

mesomeric effect of the sulfur atoms, which stabilizes the

radical cation. As expected, the outer sulfur atoms of SIET

did not show any contribution at all to the HOMO of the

radical cation, since they could never participate in a

mesomeric effect. The values obtained for the HOMO

LUMO gap followed the same trend as the UV/Vis data,

showing a larger gap for SIET (1.45 eV), than for DIET

(1.35 eV) and for ET (1.26 eV). The lower excitation

energies were also computed by the TD-DFT method; the

values obtained matched the spectroscopic results and the

previously calculated HOMO LUMO gaps (Table 2). More-

over, these theoretical calculations confirmed that this broad

and lowest energy band, observed at room temperature, must

be assigned, as in the case of ET,^[40]to the radical cation rather

than to the corresponding p-dimer.^[41]

Figure 6. Crystal structure of DIET¥ CuBr₄: top: view of the structural

layout; bottom: view of DIET², showingthe distortion of 46 8 between the

dithiolium rings.

Dications: Theoretical calculations carried out on the dication

states of BEDT-TTF, DIET, and SIET provided evidence in

this case of the existence of opposite electronic effects from

the outer sulfur atoms. Full optimization of geometry carried

out on ET²showed that the 1,3-dithiolium rings deviated by

only 0.018 from planarity, in good agreement with the

Molecular-orbital analysis performed on the optimized

geometries gave a very different picture of the HOMO

orbitals of the three dication isomers and completed the

previous observations (Figure 5). The large contribution of

the p-sulfur orbitals (S') from the ethylenedithio group (0.4

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Isomers of Tetrathiafulvalenes

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structure with alternatingplanes containinganions and

coefficient), as well as the p-orbitals of the outer carbon of the

TTF core (0.2 coefficient) and a slight contribution of the p-

orbitals of the central carbon atoms in the TTF core (0.1

coefficient) show the strong p-character of this HOMO. This

suggested a relevant argument for the existence of a

mesomeric electron-donatingeffect from the outer sulfur

atoms (S') of the ethylenedithio groups in ET². This

mesomeric effect should induce planarity of ET²and

stabilization of the dicationic state, thus explainingthe lower

measured second oxidation potential. In contrast, the main

coefficients in this HOMO orbital belongonly to the outer

sulfur atoms in DIET²and the four sulfur atoms in SIET²

(Figure 5). This important change in the electronic structure

regarding the HOMO orbitals could be associated with an

inductive electron-withdrawingeffect of the outer sulfur

atoms (S'') of the disulfide bridge(s) in DIET²and SIET²

that would remove the electronic density away from the TTF

core. It should be noted that the contribution of the sulfur

atoms (S') of the ethylenedithio group in DIET²is only slight

in orbital 96 (HOMO À1), but very important in orbital 95

(HOMO À2).

solvent molecules and planes of donors, is observed (Fig-

ure 7). Both molecules are packed in columns and form head-

to-tail, centrosymmetric dimers with short distances (3.40 and

Figure 7. Projection onto the (ab) plane of the crystal structure of DIET¥

ClO₄¥ ¹³2 C₆H₅Cl. S ¥¥¥ S contacts smaller than the sum of the van der Waals

radii are represented by dashed lines.

The lowest excitation energies obtained by the TD-DFT

method are in agreement with the measured UV/Vis absorp-

tion bands (Table 2). For the ET²dication, the HOMO

orbital still has a strong p-character and therefore the lowest

transition corresponds to the HOMO LUMO transition,

implyingmolecular orbitals 97 to 98. In contrast, the

electronic structures for DIET²and SIET²are altered

completely, and the higher orbitals become s in character. The

molecular orbitals involved in p p* transitions in DIET²

and SIET²are lower lyingin energy (molecular orbital 95

(HOMO À2) and molecular orbital 93 (HOMO À5),

respectively). Consequently, the p p* transitions for these

two dications appear higher in energy. This might also suggest

that the presence of outer sulfur atoms (S'') is responsible for

the increasing s-character of the HOMO orbitals.

3.45 ä), showingsingificant molecular overlap. However,

because of the strongtiltingof dimers from the stackingaxis

(678), weak S ¥¥¥ S interdimer interactions are present

(3.85 ä). The interestingfeature in the structure of DIET ¥

ClO₄¥ ¹³2 C₆H₅Cl salt results from the side-by-side S ¥¥¥ S

interactions alongthe a axis that are composed of: a) S ¥¥¥ S

contacts between sulfur atoms of the disulfide bridges of

neighboring donors, and b) S ¥¥¥ S contacts from sulfur atoms

of the ethylenedithio group and sulfur atoms of the TTF core,

these occur together. These interactions involving all the

outer sulfur atoms seem to be partly responsible for the

observed network in which a shift of dimers inside columns

and a shift of neighboring columns are in evidence.

In the structure of the e-BEDT-TTF ¥ ClO₄salt,^[45]in which

the formal charge on BEDT-TTF is also 1, intermolecular

S ¥¥¥ S contacts between all the outer-ringsulfur atoms ( d

3.479(4) ä) are encountered with a staggered side-by-side

mode of interaction. However, these strongS ¥¥¥ S contacts do

not imply a shift of donors in the regular stacks, in which a

face-to-face mode occurs, but with no significant intermolec-

ular interaction. As a consequence, the shift of neighboring

columns appears more important in the structure of e-BEDT-

TTF ¥ ClO₄than that observed in the structure of DIET¥

ClO₄¥ ¹³2 C₆H₅Cl.

The important torsion angle in the geometry of DIET²and

SIET²may be related to increasing s-character in the C C

central bond between the two 1,3-dithiolium moieties. This is

supported by the optimized central bond lengths, computed as

1.41 ä for ET², 1.43 ä for DIET², and 1.44 ä for SIET².

Consequently, the increase in the torsion of the central bond

and the loss of p-character are in good agreement with the

hypsochromic shift found experimentally (Table 2).

Organic materials: Radical cation salts of different stoichiom-

etries, includingmixed valence salts, derived from S-position

isomers of 1, 2, and 4 were prepared by electrocrystalliza-

tion.^{[43, 44]}To investigate the role of outer sulfur atoms in the

intermolecular contacts between p-donors, we chose three

significant examples to compare the crystallographic net-

works of two radical cation salts of identical stoichiometry

that differed only in the positions of the outer sulfur atoms on

the bridge: i) DIET¥ ClO₄¥ ¹³2 C₆H₅Cl and BEDT-TTF ¥ ClO₄,

ii) 4 ¥ ClO₄and DMTEDT-TTF ¥ ClO₄, and iii) SIET₃¥ (ClO₄)₂

and (BEDT-TTF)₃¥ (ClO₄)₂.

In conclusion, this particular organization of DIET donors

in the radical cation salt is due to the concomitant presence of

both disulfide and ethylenedithio bridges, columns of donors

beingshifted in order to engage outer sulfur atoms of the

disulfide bridge and sulfur atoms of the ethylenedithio group

in van der Waals interactions.

4 ¥ ClO₄and DMTEDT-TTF ¥ ClO₄: In the salt 4 ¥ ClO₄, donor

molecules are stacked alongthe a axis in a head-to-tail

manner, their mean molecular plane beingperpendicular to

the a axis. Inside columns, donors are dimerized, with intra-

and interdimer distances of 3.44 and 3.59 ä, respectively. The

DIET¥ ClO₄¥ ¹³2 C₆H₅Cl and BEDT-TTF ¥ ClO₄: In the DIET¥

ClO₄¥ ¹³2 C₆H₅Cl salt, as is usual in BEDT-TTF salts, a layered

Chem. Eur. J. 2001, 7, No. 23

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principal characteristic of the crystallographic network is the

tetragonal arrangement of donors in a ™windmill∫ pattern and

the localization of anions in the cavity created inside the

™windmill∫ (Figure 8).^{[8, 44a]}To our knowledge, such an array

has been only described in TTF(Z) (with Z Cl, Br, or I and

1 0.77, 0.76, or 0.77, respectively)^[46]and in the (TM-

TPDS)₂AsF₆salt.^[47]In the 4 ¥ ClO₄salt, this typical perpen-

dicular organization in the bc plane results from significant

S ¥¥¥ S contacts (3.51 and 3.55 ä) between sulfur atoms of the

donor disulfide bridge and sulfur atoms of the TTF core of

neighboring donors.

stackingaxis. Consequently, the structure of DMTEDT-TTF ¥

ClO₄may be compared to an ionic-type structure, in which

(DMTEDT-TTF)₂dimer units are surrounded by perchlo-

rate anions.

The structure of DMTEDT-TTF ¥ ClO₄, surprisingly unlike

the layered structures often encountered in EDT-TTF-de-

rived salts, also appears very different from the structure of 4 ¥

ClO₄. In the latter, the fundamental role of the outer sulfur

atoms of the donor is underlined by the establishment of the

™windmill∫ array.

SIET₃¥ (ClO₄)₂and (BEDT-TTF)₃¥ (ClO₄)₂: The association

of the symmetric S-position isomer SIETwith the ClO₄^Àanion

affords a radical cation salt with the same [3:2] stoichiometry

as that formed from BEDT-TTF [(BEDT-TTF)₃¥ (ClO₄)₂].^[48]

In the semiconductor SIET₃¥ (ClO₄)₂(s_RT 10^À2Scm^À1),

donors are organized in centrosymmetric trimers, which are

stacked alongthe a axis. Interplanar short distances (3.33 ä)

and some short S ¥¥¥ S contacts inside a trimer provided

evidence of stronginteractions between donors. Nevertheless,

the weak intertrimer molecular overlap (shorter distances of

3.745 ä) is certainly responsible for the observed semicon-

ductor behavior of this mixed-valence salt. The network is

organized in trimerized stacks and the organic columns are

oriented in the lattice so as to engage outer sulfur atoms of

both disulfide bridges in van der Waals contacts. Consequent-

ly, this salt derived from the donor SIET also displays the

characteristic ™windmill∫ array (Figure 10); this association

mode of the network beingunambiguously associated with

the presence of the terminal disulfide bridges, the arrange-

ment differingfrom the general alternation of donor layers

that characterizes BEDT-TTF salts.

Figure 8. The original ™windmill∫ network of donors 4 and disordered

ClO₄anions in the projection onto the (bc) plane of the crystal structure of

the salt 4 ¥ ClO₄.

The (BEDT-TTF)₃¥ (ClO₄)₂salt^[48]displays a layered struc-

ture, as encountered in most BEDT-TTF salts with alternating

The crystallographic network of the not previously de-

scribed DMTEDT-TTF ¥ ClO₄is characterized by dimerized

columns separated by perchlorate anions (Figure 9). Columns

are composed of face-to-face centrosymmetric dimers of

DMTEDT-TTF, in which a strongS ¥¥¥ S p-orbital overlap is

observed. In contrast, the intradimer molecular overlap is

missing, a result of the tilting of donors with regard to the

Figure 10. Projection onto the (bc) plane of the crystal structure of

(SIET)₃¥ (ClO₄)₂, characterized by the ™windmill∫ array. S ¥¥¥ S contacts

smaller than the sum of van der Waals radii are represented by dashed lines.

Figure 9. Projection onto the (bc) plane of the crystal structure of

DMTEDT-TTF ¥ ClO₄.

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Isomers of Tetrathiafulvalenes

5070 5083

potentials were found to be around Æ5 mV. UV/Vis and near-IR experi-

ments were performed with a Perkin Elmer Lambda19 NIR spectrom-

eter.

organic sheets and anion layers. In the donor array, strong

transverse side-by-side S ¥¥¥ S interactions occur, while no

intermolecular contact alongthe stackingaxis is evidenced.

Consequently, the metallic state of (BEDT-TTF)₃¥ (ClO₄)₂

became unstable, and a metal-insulator came into beingat

170 K.

2,3-Bis(acetylthiomethyl)-6,7-bis(methylsulfanyl)tetrathiafulvalene (10a):

Diethyl azodicarboxylate (0.64 mL, 4 mmol) was added dropwise at 08C

under argon to a solution of triphenylphosphine (1.05 g, 4 mmol) in

anhydrous THF (5 mL). After this mixture had been stirred at 08C for

15 min, a solution of 2,3-bis(hydroxymethyl)TTF (5a, 0.356 g, 1 mmol) and

thioacetic acid (0.29 mL, 4 mmol) in THF (15 mL) was added dropwise.

The dark solution was stirred at 08C for 1 h and then at room temperature

for 1 h. The reaction mixture was dissolved in CH₂Cl₂(150 mL) and washed

with water (3 Â 60 mL). The organic phase was dried (MgSO₄) and

concentrated, and the residue was purified by flash column chromatog-

raphy (silica gel, petroleum ether/CH₂Cl₂1:1). Recrystallization (CH₂Cl₂/

petroleum ether) gave orange crystals of the bis(thiolester)TTF 10a. Yield:

0.274 g, 58%; m.p. 104 1068C; ¹H NMR (200 MHz, CDCl₃): d 3.95 (s,

4H; CH₂S), 2.40 (s, 6H; SCH₃), 2.38 (s, 6H; COCH₃); ¹³C NMR (50 MHz,

Conclusion

Efficient and original synthetic methodologies for obtaining

different S-position isomers of BEDT-TTF and EDT-TTF,

introducingouter disulfide rin(gs) on the TTF core, are

described. Their p-donor ability makes them good candidates

for the preparation of organic metals. Firstly, the electronic

effect of the peripheral sulfur atoms× positions were clearly

demonstrated by a correlation between electrochemical and

spectroscopic studies, completed with theoretical calculations

on neutral and oxidized states. Secondly, the role of the

terminal disulfide bridge(s) in the association mode of the

network was established. Despite the poor contribution of

outer sulfur atoms of the disulfide bridge in the HOMO, most

of the electrogenerated radical cation salts display interesting

structural features, with evidence of S ¥¥¥ S contacts that are

responsible for the crystallographic organization of donors,

especially in the case of the characteristic ™windmill∫ organ-

ization. While most of the resultingmaterials exhibit semi-

conductor behavior, electro-oxidations in the presence of

various anions are currently under investigation. The role of

peripheral sulfur atoms in the solid state network havingbeen

demonstrated, other radical cation salts with two-dimensional

or even three-dimensional structural organizations are to be

expected in the future from this new promisingseries of p-

donors.

CDCl₃): d 194.20 (2C; C O), 30.32 (2C; COCH₃), 26.54 (2C; C-CH₂-S),

19.16 (2C; SCH₃); IR (KBr): nÄ 1683 and 1698 cm^À1(C O); MS (70 eV,

EI): m/z (%): 472 (62) [M] , 322 (95), 307 (15), 249 (23), 97 (30), 83 (35),

69 (44), 57 (51), 55 (56), 43 (100); elemental analysis calcd (%) for

C₁₄H₁₆S₈O₂(472.76): C 35.57, H 3.41, S 54.25; found C 35.69, H 3.35, S 54.07.

2,3-Bis(acetylthiomethyl)-6,7-(ethylenedisulfanyl)tetrathiafulvalene

(10b): N,N-Dimethylformamide diethyl acetal (1.4 mL, 8 mmol) and

thioacetic acid (0.58 mL, 8 mmol) were added to a solution of 2,3-

bis(hydroxymethyl)TTF (5b, 0.354 g, 1 mmol) in anhydrous CH₂Cl₂

(70 mL). The solution was stirred at reflux for 48 h under nitrogen. The

reaction mixture was diluted with CH₂Cl₂(100 mL), washed with water

(2 Â 100 mL), dried (MgSO₄), and concentrated. The residue was purified

by flash column chromatography (silica gel, petroleum ether/EtOAc 4:1) to

afford yellow-ochre crystals after recrystallization (petroleum ether/

EtOAc). Yield: 0.280 g, 60%; m.p. 124 1268C; ¹H NMR (200 MHz,

CDCl₃): d 3.94 (s, 4H; -CH₂S-CO), 3.27 (s, 4H; SCH₂CH₂S), 2.37 (s, 6H;

COCH₃); C NMR (50 MHz, CDCl₃): d 194.24 (2C; C O), 30.32 (2C;

COCH₃), 30.26 (SCH₂CH₂S), 26.47 (2C; C-CH₂-S); MS (70 eV, EI): m/z

(%): 470 (51) [M] , 442 (17), 322 (17), 320 (44), 292 (16), 88 (21), 43 (100);

elemental analysis calcd (%) for C₁₄H₁₄S₈O₂(470.78): C 35.71, H 3.00, S

54.49; found C 35.81, H 2.93, S 54.29.

2,3-(2,3-Dithiabutane-1,4-diyl)-6,7-(ethylenedisulfanyl)tetrathiafulvalene

(1): A solution of the bis(thioester)TTF 10b (71 mg, 0.15 mmol) in dry

THF (10 mL) was added dropwise at 08C under nitrogen to a suspension of

sodium borohydride (38 mg, 1 mmol) and anhydrous lithium chloride

(5 mg, 0.1 mmol) in dry THF (10 mL). The reaction mixture was allowed to

reach room temperature and was then stirred at reflux for 1 h. The solution

was cooled to 08C and quenched with ice-water (5 mL) and a saturated

solution of ammonium chloride (10 mL). The reaction mixture was stirred

overnight at room temperature to precipitate compound 1. The orange

crystals were filtered, washed several times with dry methanol, and dried

under vacuum to afford analytically pure DIET (1, 51 mg, 88%). Further

purification could be achieved by Soxhlet extraction with CS₂for several

days. M.p. 236 2388C; ¹H NMR (200 MHz, CS₂ CDCl₃): d 3.45 (s, 4H;

CH₂SSCH₂), 3.27 (s, 4H; SCH₂CH₂S); MS (70 eV, EI): m/z (%): 384 (15)

Experimental Section

General procedures: The followingchemicals were obtained commercially

and were used without any purification. Dry solvents were obtained by

distillation over suitable desiccants (THF and toluene from Na/benzophe-

none, CH₂Cl₂from P₂O₅, CH₃CN from CaH₂). Thin-layer chromatography

(TLC) was performed on aluminium sheets coated with 60F₂₅₄silica gel

(Merck 5554). Column chromatography was carried out on 60 silica gel

(Merck 9385, 230 400 mesh) or Florisil (Acros, 100 200 mesh). Melting

points were determined by usinga microscope with a Kofler hot stage and

are uncorrected. ¹H and ¹³C NMR spectra were recorded on a Brucker

AC200 (200 MHz) spectrometer. Chemical shifts are reported as d values

in ppm downfield from internal TMS. In ¹³C NMR spectra, only character-

istic peaks are reported. Mass spectra were recorded on a HP5889A

[M] , 322 (32), 320 (100), 294 (17), 292 (64), 216 (15), 172 (47), 88 (45), 76

(57), 64 (22), 52 (33); elemental analysis calcd (%) for C₁₀H₈S₈(384.692): C

31.22, H 2.10, S 66.68; found C 30.98, H 2.09, S 66.09.

2,3-(2,3-Dithiabutane-1,4-diyl)-6,7-bis(methylsulfanyl)tetrathiafulvalene

(4): This compound was prepared by the same experimental procedure that

afforded 1, with NaBH₄/LiCl. At the end of the reaction, after hydrolysis

and extraction with EtOAc, the residue was purified by column chroma-

tography (silica gel, petroleum ether/CH₂Cl₂1:1) to afford orange-red

crystals. Yield: 93%; m.p. 173 1748C; ¹H NMR (200 MHz, CDCl₃): d

3.48 (s, 4H; CH₂SSCH₂), 2.42 (s, 6H; SCH₃); ¹³C NMR (50 MHz, CDCl₃):

d 30.42 (2C; CH₂SSCH₂), 19.20 (2C; SCH₃); MS (70 eV, EI): m/z (%):

spectrometer at 70 eV. IR spectra were recorded with

a Brucker

IFS45WHR spectrometer. Elemental microanalyses were performed by

the Central Service of Microanalysis of the CNRS (Vernaison, France).

Cyclic voltammetry was performed in a three-electrode cell equipped with

a platinum millielectrode of 7.85 Â 10^À3cm²area and a platinum wire

counter electrode. An Ag/AgCl electrode checked against the ferrocene/

ferricinium couple before and after each experiment was used as reference.

The electrolytic media involved CH₂Cl₂(HPLC grade) and 5 Â 10^À1molL^À1

tetrabutylammonium hexafluorophosphate (TBAHP–Fluka puriss qual-

ity). All experiments were carried out in solutions previously degassed by

argon bubbling at 298 Æ 0.5 K. Electrochemical experiments were carried

out with an EGGPAR273A potentiostat with positive feedback compen-

sation. On the basis of repetitive measurements, absolute errors on

386 (16) [M] , 324 (29), 322 (100), 307 (29), 274 (16), 172 (21), 118 (13), 103

(12), 91 (14), 88 (14); elemental analysis calcd (%) for C₁₀H₁₀S₈(386.708): C

31.06, H 2.61, S 66.34; found C 31.16, H 2.52, S 65.85.

4,5-Bis(bromomethyl)-2-thioxo-1,3-dithiole

(12a):

PBr₃

(0.31 mL,

3.25 mmol) was added dropwise to a solution of the diol 6a (450 mg,

2.32 mmol) dissolved in anhydrous THF (5 mL) and anhydrous CCl₄

(10 mL). The resultinglight solution and orange precipitate were stirred

Chem. Eur. J. 2001, 7, No. 23

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P. Hudhomme et al.

FULL PAPER

under argon at room temperature for 5 h. The reaction mixture was treated

with aqueous HCl (3n, 15 mL), washed twice with aqueous NaHCO₃(1m,

15 mL) and once with brine (15 mL), dried (MgSO₄), and evaporated. The

residue was purified by flash chromatography (silica gel, CH₂Cl₂) to afford

12a as a yellow powder, which was a slight irritant and unstable after

several weeks in the fridge. Yield: 690 mg, 93%; m.p. 1268C (CH₂Cl₂);

¹H NMR (200 MHz, CDCl₃): d 4.33 (s, CH₂); ¹³C NMR (50 MHz, CDCl₃):

4,5-(2,3-Dithiabutane-1,4-diyl)-2-oxo-1,3-dithiole (13b): A solution of

MeONa/MeOH prepared from sodium (25 mg, 1.1 mmol) in anhydrous

MeOH (2 mL) under nitrogen at room temperature was added to a solution

of 11b (150 mg, 0.51 mmol) in anhydrous MeOH (2 mL). The solution was

stirred for 5 min and treated with a solution of iodine (66 mg, 0.26 mmol) in

anhydrous Et₂O (2 mL). After an additional 5 min of stirring, the mixture

was treated with an NH₄Cl solution (15 mL). The organic layer was

extracted twice with EtOAc (10 mL), washed with a Na₂S₂O₃solution

(20 mL) and water (20 mL), dried (MgSO₄), and evaporated. Purification

by filtration on silica gel (petroleum ether/EtOAc 1:1) afforded the

d 208.0 (1C; C S), 139.4 (2C; C C), 20.2 (2C; CH₂); IR (KBr): nÄ 1064

À1

(C S); 593 cm (C Br); MS (70 eV, EI): m/z (%): 322/320/318 [M] (29/

48/24), 241/239 (100/85), 165/163 (34/35), 84 (96), 58 (82); elemental

analysis calcd (%) for C₅H₄S₃Br₂(320.075): C 18.76, H 1.26, S 30.05, Br

49.93; found C 18.92, H 1.25, S 28.75, Br 50.03.

disulfide 13b as an orange oil. Yield: 90 mg, 85%; H NMR (CDCl₃): d

3.64 (s, CH₂); C NMR (CDCl₃): d 187.1 (1C; C O), 129.7 (2C; C C),

À1

29.2 (2C; CH₂); IR (KBr): nÄ 1685 (C O), 1646 cm (C C); MS (EI): m/z

4,5-Bis(acetylthiomethyl)-2-thioxo-1,3-dithiole (11a): a) Thioacetic acid

(1.13 mL, 16.1 mmol) and pyridine (1.32 mL, 16.1 mmol) were added

under nitrogen at room temperature to a solution of 12a (2.34 g, 7.31 mmol)

in anhydrous THF (80 mL); this resulted in a brown precipitate. The

mixture was stirred for 2 h 30 min and heated under refluxed for an

additional hour. After removal of the precipitate by filtration, the solvent

was evaporated and purification by column chromatography (silica gel,

petroleum ether/CH₂Cl₂1:1, then CH₂Cl₂) afforded compound 11a as

yellow crystals (2.14 g, 94%) after recrystallization from EtOAc/petroleum

ether.

(%): 208 [M] (100), 144 (61), 116 (48), 70 (17), 58 (32).

2,3,6,7-Tetrakis(acetylthiomethyl)tetrathiafulvalene (14): a) Coupling

from the dithiolium salt 17: Triethylamine (2.4 mL, 17.4 mmol) was added

at room temperature to a solution of the dithiolium salt 17 (3.19 g,

8.71 mmol) in anhydrous CH₃CN (15 mL) under argon. The resulting

colorless solution and brown precipitate were stirred for 1 h. After addition

of water (50 mL) and stirringfor an additional 1 h, the precipitate was

filtered off and washed with water. Purification by a filtration on Florisil

(CH₂Cl₂) afforded TTF 14 as orange fibers (1.50 g, 62%) after recrystal-

lization from THF/petroleum ether.

b) Potassium thioacetate (3.55 g, 31.2 mmol) was added to a solution of 12a

(4.53 g, 14.16 mmol) in anhydrous THF (180 mL) under nitrogen. After this

had been heated under reflux for 90 min, the precipitate was removed by

filtration. The solvent was evaporated, and purification by column

chromatography (silica gel, petroleum ether/CH₂Cl₂1:1, then CH₂Cl₂)

afforded 11a as yellow crystals after recrystallization from EtOAc/

petroleum ether. Yield: 4.00 g, 91%; m.p. 748C ; ¹H NMR (200 MHz,

CDCl₃): d 4.08 (s, 4H; CH₂), 2.40 (s, 6H; CH₃); ¹³C NMR (50 MHz,

b) Substitution of the tetrakis(hydroxymethyl)TTF (5d): N,N-Dimethylform-

amide diethyl acetal (0.82 mL, 4.8 mmol) and thioacetic acid (0.34 mL,

4.8 mmol) were successively added to a solution of tetrakis(hydroxy-

methyl)TTF 5d^[11b](97 mg, 0.30 mmol) in anhydrous THF (25 mL). The

reaction mixture was heated under reflux for 48 h under argon. After

dilution with CH₂Cl₂(50 mL), the solution was washed with water (3 Â

30 mL), dried (MgSO₄), and evaporated. The residue was filtered on

Florisil (CH₂Cl₂/EtOAc 4:1), and recrystallization from EtOAc/petroleum

ether gave TTF 14. Yield: 104 mg, 63%; m.p. 2178C (THF/petroleum

ether); ¹H NMR (200 MHz, CDCl₃): d 3.92 (s, 8H; CH₂), 2.37 (s, 12H;

CDCl₃): d 210.4 (1C; C S), 193.6 (2C; C O), 138.5 (2C; C C), 30.2 (2C;

À1

CH₃), 25.6 (2C; CH₂); IR (KBr): nÄ 1699 (C O), 1686 (C O), 1070 cm

(C S); MS (70 eV, EI): m/z (%): 310 [M] (23), 234 (28), 193 (33), 59 (19),

43 (100); elemental analysis calcd for C₉H₁₀O₂S₅(310.477): C 34.82, H 3.25,

S 51.63; found C 34.90, H 3.16, S 51.66.

CH₃); ¹³C NMR (50 MHz, CDCl₃): d 194.6 (4C; C O), 128.9 (4C; C C),

108.1 (2C; central C C), 30.2 (4C; CH₃), 26.1 (4C; CH₂); IR (KBr): nÄ

1688 cm^À1(C O); MS (70 eV, EI): m/z (%): 556 [M] (22), 406 (43), 288

(21), 43 (100); elemental analysis calcd for C₁₈H₂₀O₄S₈(556.834): C 38.83, H

3.62, S 46.06; found C 38.80, H 3.57, S 45.55.

4,5-Bis(acetylthiomethyl)-2-oxo-1,3-dithiole (11b): a) A solution of 12b^[23]

(1.65 g, 5.43 mmol) in anhydrous THF (60 mL) was added to a well-stirred

solution of thioacetic acid (0.84 mL, 12 mmol) and pyridine (1 mL,

12 mmol) in anhydrous THF (60 mL). The mixture was heated under

reflux under nitrogen. A white precipitate was observed, and heating under

reflux was continued for 3 h. The mixture was allowed to cool to room

temperature, and the precipitate was removed by filtration. The solvent was

evaporated, and purification by column chromatography on silica gel

(CH₂Cl₂) afforded compound 11b as beige crystals (1.57 g, 98%).

2,3,6,7-Bis(2,3-dithiabutane-1,4-diyl)tetrathiafulvalene (2): A solution of

MeONa/MeOH, prepared from sodium (54 mg, 2.38 mmol) in anhydrous

MeOH (4 mL) under argon, was added at room temperature to

suspension of compound 14 (300 mg, 0.54 mmol) in anhydrous MeOH/

DMF (44 mL, 10:1) and the mixture was heated to 408C for 1 h. The orange

suspension changed to a red precipitate, which was filtered off and washed

with CH₂Cl₂and EtOAc. Purification by filtration on silica gel (CS₂)

afforded SIET (2) as a pink powder. Yield: 130 mg, 63%; m.p. 2208C;

¹H NMR (200 MHz, CDCl₃ CS₂): d 3.45 (s, CH₂); ¹³C NMR (50 MHz,

b) A solution of 12b (140 mg, 0.46 mmol) in anhydrous THF (7.5 mL) was

added to a well-stirred solution of potassium thioacetate (116 mg, 1 mmol)

in anhydrous THF (7.5 mL), the mixture was heated under reflux under

nitrogen. A white precipitate quickly formed, and the resulting brown

solution then became darker and darker while heated under reflux for 15 h.

After cooling, the solvent was evaporated, and purification by column

chromatography on silica gel (petroleum ether/CH₂Cl₂1:1, then CH₂Cl₂)

afforded compound 11b. Yield: (120 mg, 89%; m.p. 76 778C; ¹H NMR

(200 MHz, CDCl₃): d 4.12 (s, 4H; CH₂), 2.39 (s, 6H; CH₃); ¹³C NMR

C₆D₆ CS₂): d 123.5 (4C; C C); 105.6 (2C; central C C); 31.0 (4C;

À1

CH₂); Raman: nÄ 1542 (C C); 511 cm (S S); MS (70 eV, EI): m/z (%):

384 [M] (39), 320 (67), 256 (100), 172 (25), 128 (18), 52 (22); elemental

analysis calcd for C₁₀H₈S₈(384.655): C 31.22, H 2.10, S 66.68; found C 31.25,

H 2.06, S 66.59.

4,5-Bis(acetylthiomethyl)-2-methylsulfanyl-1,3-dithiolium trifluorometh-

anesulfonate (15): Methyl trifluoromethanesulfonate (1.22 mL, 11.6 mmol)

was added at room temperature to a solution of thione 11a (3 g, 9.68 mmol)

in anhydrous CH₂Cl₂(15 mL) under nitrogen. The resulting dark solution

was stirred for 4 h, anhydrous Et₂O (50 mL) was then added, and the

solution was left in the fridge overnight. After removal of the ethereal

liquid, the resultingoil was dried under vacuum to yield the dithiolium salt

15 as brown crystals. Yield: 4.5 g, 98%; m.p. 43 448C (Et₂O); ¹H NMR

(200 MHz, CDCl₃): d 4.47 (s, 4H; CH₂), 3.17 (s, 3H; SCH₃), 2.44 (s, 6H;

CH₃); ¹³C NMR (50 MHz, CDCl₃): d 203.2 (1C; CSCH₃), 194.9 (2C;

(50 MHz, CDCl₃): d 193.8 (2C; C O), 189.8 (1C; C O), 127.0 (2C;

C C), 30.2 (2C; CH₃), 26.3 (2C; CH₂); IR (KBr): nÄ 1682 (C O),

1619 cm^À1(C O); MS (70 eV, EI): m/z (%): 294 [M] (4), 218 (32), 175

(20), 43 (100); elemental analysis calcd for C₉H₁₀O₃S₄(294.416): C 36.72, H

3.42, S 43.56; found C 36.63, H 3.33, S 43.42.

4,5-(2,3-Dithiabutane-1,4-diyl)-2-thioxo-1,3-dithiole (13a): A solution of

11a (155 mg, 0.5 mmol) in anhydrous THF (30 mL) was added to a solution

of sodium borohydride (127 mg, 3.2 mmol) and anhydrous lithium chloride

(16.5 mg, 0.39 mmol) in anhydrous THF (10 mL) under nitrogen. After

beingheated under reflux for 3 h, the solution was cooled to 0 8C and then

quenched with a saturated solution of ammonium chloride (20 mL). The

reaction mixture was stirred overnight at room temperature. After

extraction with EtOAc, the residue was purified by column chromatog-

raphy (silica gel, CH₂Cl₂) to afford yellow crystals. Yield: 87 mg, 78%; m.p.

C O), 149.5 (2C; C C), 29.9 (2C; CH₃), 26.1 (2C; CH₂), 22.9 (1C; SCH₃);

IR (KBr): nÄ 1693 cm^À1(C O); MS (FAB): 325 [M] ; elemental analysis

calcd for C₁₁H₁₃O₅S₆F₃(474.58): C 27.84, H 2.76; found C 26.94, H 2.68.

4,5-Bis(acetylthiomethyl)-2-methylsulfanyl-1,3-dithiole (16): Sodium bor-

ohydride (336 mg, 8.44 mmol) was cautiously added to a solution of the

dithiolium salt 15 (4 g, 8.44 mmol) in anhydrous CH₃CN (40 mL) and

iPrOH (6 mL) under argon at 08C. The mixture was allowed to reach room

temperature and stirred for 4 h. Purification by column chromatography

151 1528C (CH₂Cl₂); H NMR (CDCl₃): d 3.68 (s, CH₂); MS (EI): 224

[M] (100), 160 (60), 96 (11), 84 (24), 69 (13), 58 (30).

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Chem. Eur. J. 2001, 7, No. 23

Isomers of Tetrathiafulvalenes

5070 5083

(silica gel, petroleum ether/EtOAc 8:2) afforded compound 16 as beige

crystals. Yield: 2.5 g, 91%; m.p. 508C (EtOAc); ¹H NMR (200 MHz,

95 mg, 17%; this represented an overall yield of 90%. M.p. 90 918C

(EtOAc/hexane); H NMR (200 MHz, CDCl₃): d 6.29 (s, 2H; CH CH),

CDCl₃): d 5.78 (s, 1H; CH), 4.02 and 3.87 (2d, J_ABsyst. 14.4 Hz, 4H;

3.95 (s, 4H; CH₂), 2.38 (s, 6H; CH₃); ¹³C NMR (50 MHz, CDCl₃): d 194.3

CH₂), 2.37 (s, 6H; CH₃), 2.23 (s, 3H; SCH₃); ¹³C NMR (50 MHz, CDCl₃):

(2C; C O), 128.5 (2C; C C), 119.1 (2C; CH), 30.3 (2C; CH₃), 26.5 (2C;

d 195.2 (2C; C O), 125.0 (2C; C C), 56.8 (1C; CH), 30.1 (2C; CH₃), 26.5

CH₂); MS (EI): m/z (%): 380 [M] (47), 305 (10), 262 (30), 230 (100), 146

(42), 102 (32), 43 (54); elemental analysis calcd for C₁₂H₁₂O₂S₆(380.586): C

37.87, H 3.18, S 50.54; found C 37.90, H 3.12, S 50.01.

(2C; CH₂), 11.4 (1C; SCH₃); IR (KBr): nÄ 1687 cm^À1(C O); MS (70 eV,

EI): m/z (%): 326 [M] (12), 279 (100), 237 (61), 195 (31), 161 (37), 129

(54), 43 (83); elemental analysis calcd for C₁₀H₁₄O₂S₅(326.52): C 36.78, H

4.32; found C 36.80, H 4.31.

2,3-(2,3-Dithiabutane-1,4-diyl)tetrathiafulvalene (3): Sodium borohydride

(64 mg, 1.7 mmol) and anhydrous lithium chloride (10 mg, 0.25 mmol) were

added to a solution of the bis(thioester)TTF 10c (95 mg, 0.25 mmol) in

anhydrous THF (20 mL) under nitrogen. The solution was heated under

reflux overnight, then quenched with a saturated ammonium chloride

solution (10 mL). The product was extracted with EtOAc (100 mL),

washed with brine (3 Â 30 mL), dried (MgSO₄), and concentrated. Purifi-

cation by filtration on Florisil (petroleum ether/EtOAc 4:1) afforded

disulfide 3 as orange crystals after recrystallization from EtOAc/petroleum

ether. Yield: 20 mg, 28%; m.p. 1748C; ¹H NMR (200 MHz, CDCl₃): d

4,5-Bis(acetylthiomethyl)-1,3-dithiolium tetrafluoroborate (17): A solution

of tetrafluoroboric acid in Et₂O (54% wt.%, 2.11 mL, 8.4 mmol) was added

at 08C to a solution of compound 16 (2.5 g, 7.67 mmol) in acetic anhydride

(15 mL) under argon. The resulting dark solution was stirred for 1 h.

Anhydrous Et₂O (120 mL) was then added, and the solution was left in the

fridge overnight. After removal of the ethereal liquid, the resulting oil was

dried under vacuum to yield the dithiolium salt 17 as dark crystals. Yield:

2.79 g, 99%; m.p. 528C (Et₂O); H NMR (200 MHz, CDCl₃): d 11.08 (s,

6.32 (s, 2H; CH CH), 3.75 (s, 4H; CH₂); ¹³C NMR (50 MHz, CDCl₃): d

1H; CH), 4.57 (s, 4H; CH₂), 2.43 (s, 6H; CH₃); ¹³C NMR (50 MHz, CDCl₃):

123.1 (2C; C C); 119.1 (2C; CH); 118.5 (2C; C C); 111.8 (2C; central

d 195.0 (1C; CH), 175.8 (2C; C O), 156.4 (2C; C C), 30.0 (2C; CH₃),

25.8 (2C; CH₂); IR (KBr): nÄ 1694 cm^À1(C O); MS (FAB): 279 [M] ;

C C); 30.4 (2C; CH₂); MS (EI): m/z (%): 294 [M] (29), 230 (100), 154

(21), 146 (30), 102 (39); elemental analysis calcd for C₈H₆S₆(294.495): C

32.63, H 2.05, S 65.32; found C 32.69, H 2.01, S 65.27; CV (CH₂Cl₂/CH₃CN

9:1, 1.4 Â 10^À3m, V vs Ag/AgCl) Ep_a1 0.484, Ep_a2 0.944, Ep_c1 0.455,

Ep_c2 0.918, compared with EDT-TTF: (CH₂Cl₂/CH₃CN 9:1, 1.4 Â 10^À3m,

V vs Ag/AgCl) Ep_a1 0.476, Ep_a2 0.907, Ep_c1 0.455, Ep_c2 0.887.

elemental analysis calcd for C₉H₁₁O₂S₄F₄B (366.25): C 29.51, H 3.03; found

C 29.33, H 3.15.

Phosphonium salt 19: Triphenylphosphine (530 mg, 2 mmol) was added at

room temperature to a solution of the dithiolium salt 17 (730 mg, 2 mmol)

in anhydrous CH₃CN (25 mL) under argon, and the mixture was stirred for

3 h. Anhydrous Et₂O (150 mL) was then added, and the solution was left

overnight in the fridge. After removal of the ethereal liquid, the resulting

dark oil was dried under vacuum to give the phosphonium salt 19 as a beige

The followingcrystal structures have been deposited at the Cambridge

Crystallographic Data Centre and allocated the deposition numbers

CCDC 163955 163957:

Salt DIET¥ CuBr₄: P2₁/n, a 6.639(4), b 22.113(8), c 14.015(9) ä, b

99.93(5)8, V 2026(3) ä³, Z 4, 1_calcd 2.52 gcm^À3, l(Mo_Ka) 0.71073 ä,

2059 reflections (2 < q < 208) were collected at 298 K, 721 with I > 2s(I)

used in refinements, 118 refined parameters, R 0.059, Rw 0.066.

mass. Yield: 1.23 g, 98%; H NMR (200 MHz, CDCl₃): d 9.37 (m, 15H;

CH arom.), 7.20 (d, ²J(H,P) 4.6 Hz, 1H; CH), 3.43 and 3.26 (2d, ²J_ABsyst.

14.9 Hz, 4H; CH₂), 2.30 (s, 6H; CH₃); ¹³C NMR (50 MHz, CDCl₃): d

193.9 (2C; C O), 135.4 115.5 (CH arom. and C C), 40.6 (d, ¹J(C,P)

42 Hz, 1C; CH), 30.3 (2C; CH₃), 26.0 (2C; CH₂); IR (KBr): nÄ 1695 cm^À1

(DMTEDT-TTF) ¥ ClO₄: Single crystals of (DMTEDT-TTF) ¥ ClO₄(1.1 Â

0.3 Â 0.1 mm) were grown at 48C on a platinum-wire anode by oxidation of

the donor in a solution of Bu₄NClO₄(0.1m in chlorobenzene/EtOH 9:1 at

constant low-current density (2 mAcm^À2). Triclinic, P1, a 8.144(3), b

10.172(2), c 11.116(2) ä, a 83.48(1)8, b 74.57(2)8, g 86.92(2)8, V

881.6(4) ä³, Z 2, 1_calcd 1.831 gcm^À3, l(Mo_Ka) 0.71073 ä, 5462 reflec-

tions (2 < q < 308) were collected at 298 K, 3088 with I > 3s(I) used in

refinements, 208 refined parameters, R 0.061, Rw 0.095.

(C O); elemental analysis calcd for C₂₇H₂₆O₂S₄PF₄B (628.52): C 51.59, H

4.17, S 20.41, P 4.93; found C 51.41, H 4.21, S 19.87, P 4.75.

2,3-Bis(acetylthiomethyl)tetrathiafulvalene (10c): a) Method using the

Mitsunobu reaction: Diethyl azodicarboxylate (0.64 mL, 4 mmol) was

added dropwise at 08C to a solution of triphenylphosphine (1.05 g, 4 mmol)

in anhydrous THF (9 mL) under argon. After this had stirred at 08C for

15 min, a solution of 2,3-bis(hydroxymethyl)TTF (5c, 0.132 g, 0.5 mmol)

and thioacetic acid (0.29 mL, 4 mmol) in anhydrous THF (10 mL) was

added dropwise. The resultingdark solution was stirred at 0 8C for 1 h and

then at room temperature overnight. The reaction mixture was dissolved in

EtOAc (150 mL), washed with brine (3 Â 30 mL), and dried (MgSO₄), and

the solvent was evaporated. The residue was purified by column

chromatography on silica gel (hexane/EtOAc 7:3) to afford the TTF 10c

as yellow-ochre crystals (0.097 mg, 51%) after recrystallization from

EtOAc/hexane.

(DIET) ¥ ClO₄¥ ¹³2 C₆H₅Cl: Single crystals of (DIET) ¥ ClO₄¥ ¹³2 C₆H₅Cl

(0.6 Â 0.3 Â 0.1 mm) were grown at 68C on a platinum-wire anode by

oxidation of the donor in a solution of Bu₄NClO₄(0.1m) in chlorobenzene/

CH₃CN (8:2) at constant low-current density (1 mAcm^À2). Triclinic, P, a

9.355(5), b 10.133(3), c 11.732(5) ä, a 105.17(3)8, b 99.36(4)8, g

104.92(3)8, V 1005.1(8) ä³, Z 2, 1_calcd 1.785 gcm^À3

l(Mo_Ka)

0.71073 ä, 3741 reflections (2 < q < 258) were collected at 298 K, 1803

with I > 3s(I) used in refinements, 262 refined parameters, R 0.064, Rw

0.085.

b) Method using dithiolium salts: Anhydrous triethylamine (12 mL) was

added dropwise over a period of 5 min to a solution of the dithiolium salt

18^[29](0.570 g, 3 mmol) and the dithiolium salt 17 (1.098 g, 3 mmol) in

anhydrous CH₃CN (75 mL) at 08C. After stirringat 0 8C for 30 min, the

solution was allowed to come up to room temperature over 2.5 h and then

concentrated. The residue was dissolved in EtOAc (50 mL) and toluene

(50 mL) and the solution was concentrated. The compounds were

separated by usingchromatorgaphy on silica egl [toluene for TTF,

toluene/EtOAc (9:1) for dissymmetric TTF 10c, then toluene/EtOAc

(7:3) for tetrakis(thioester)TTF] and were obtained in the following

amounts: TTF/10c/14 0.142 mg, 23%/0.502 mg, 44%/0.298 mg, 18%; this

represented an overall yield of 85%.

Acknowledgement

Financial support was provided by the CNRS, MENRT (research student-

ship to C.D.), and the Ville d×Angers (grant to S.L.M.). We thank Fatia

Belarbi for preliminary theoretical calculations on the neutral state of

BEDT-TTF and its S-position isomers.

[1] For recent reviews see: a) J. L. Segura, N. MartÌn, Angew. Chem. 2001,

113, 1416 1455; Angew. Chem. Int. Ed. 2001, 40, 1372 1409; b) M. R.

Bryce, J. Mater. Chem. 2000, 10, 589 598; c) M. B. Nielsen, C.

Lomholt, J. Becher, Chem. Soc. Rev. 2000, 29, 153 164; d) M. R.

Bryce, Adv. Mater. 1999, 1, 11 23; e) J. Becher, J. Lau, P. M˘rk,

Electronic Materials: The Oligomeric Approach (Eds.: K. M¸llen, G.

Wegner), Wiley-VCH, Weinheim, 1998.

[2] a) J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser,

H. H. Wang, A. M. Kini, M. H. Whangbo, Organic Superconductors

(Including Fullerenes), Prentice Hall, Englewood Cliffs, New Jersey,

1992; b) Organic Conductors. Fundamentals and Applications (Ed.:

c) Method using dithiolium and phosphonium salts: Triphenylphosphine

(265 mg, 1 mmol) was added under nitrogen to a solution of the dithiolium

salt 18^[29](190 mg, 1 mmol) in anhydrous CH₃CN. After this had stirred for

1 h, the dithiolium salt 17 (365 mg, 1 mmol) in anhydrous CH₃CN (15 mL)

was added before dropwise addition of anhydrous triethylamine (1 mL).

After the solution had been stirred at room temperature for 30 min it was

concentrated. The residue was purified by column chromatography on

silica gel [petroleum ether/CH₂Cl₂(3:7) for TTF, CH₂Cl₂for dissymmetric

TTF 10c, then CH₂Cl₂/EtOAc (9:1) for tetrakis(thioester)TTF] and the

followingamounts were obtained: TTF/ 10c/14 20 mg, 10%/237 mg, 63%/

Chem. Eur. J. 2001, 7, No. 23

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FULL PAPER

J. P. Farges), Marcel Dekker, New York, 1994; c) H. Mori, Int. J. Mod.

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Isomers of Tetrathiafulvalenes

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Received: May 25, 2001 [F3287]

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